Conducted communication in a medical device system

ABSTRACT

An implantable medical device for implantation into a patient may include a housing, a pulse generation circuit disposed at least partially within the housing, a plurality of electrodes electrically coupled to the pulse generation circuit, the plurality of electrodes being exposed external to the housing, and a controller operatively coupled to the pulse generation circuit. The controller may be configured to command the pulse generation circuit to deliver a phasic conducted communication pulse via at least two of the plurality of electrodes. Additionally, the phasic conducted communication pulse may comprise a first phase having a first polarity followed by a second phase having an opposite second polarity, wherein the second phase may have a duration of less than 60 microseconds, and wherein the first phase having may have a duration of between five percent and eighty percent of the duration of the second phase.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/268,751 filed on Dec. 17, 2015, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to medical devices, and more particularly to conducted communications between medical devices in a multi-device system.

BACKGROUND

Implantable medical devices are commonly used to monitor, diagnose and/or treat various conditions in the body. Such devices can include, for example, neuro-stimulators, diagnostic devices, chemical sensors, pressure sensors, temperature sensors, etc. Pacing devices are another example. Pacing devices are used to treat patients suffering from various heart conditions. Many heart conditions can lead to rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these heart conditions, various cardiac stimulating/sensor devices (e.g., pacemakers, defibrillators, etc.) are often implanted into a patient's body. Such devices are then used to monitor and provide electrical stimulation to the heart to help the heart operate in a more normal, efficient and/or safe manner.

Regardless of the type of implantable device, it is often desirable to establish communication with the implanted device. In some cases, conducted communication is used, which relies on electrical communication signals or pulses that “conducted” through the body. In some cases, such electrical communication signals or pulses can undesirably stimulated body tissue. What would be desirable is an improved conducted communication scheme that is less likely to stimulate body tissue.

SUMMARY

The present disclosure generally relates to systems, devices, and methods for communicating with or between implantable medical devices. In a first illustrative embodiment, an implantable medical device for implantation into a patient may comprise a housing, a pulse generation circuit disposed at least partially within the housing, a plurality of electrodes electrically coupled to the pulse generation circuit, the plurality of electrodes being exposed external to the housing, and a controller operatively coupled to the pulse generation circuit. In some instances, the controller may be configured to command the pulse generation circuit to deliver a phasic conducted communication pulse via at least two of the plurality of electrodes. The phasic conducted communication pulse may comprise a first phase having a first polarity followed by a second phase having an opposite second polarity. The second phase may have a duration of less than 60 microseconds. In some cases, the first phase may have a duration of between five percent and eighty percent of the duration of the second phase.

Additionally, or alternatively, the first phase may have a first phase amplitude, where the absolute value of the first phase amplitude may be between 1 and 15 volts.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the second phase may have a second phase amplitude, where the absolute value of the second phase amplitude may be between 1 and 15 volts.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the first phase may have a first phase amplitude with an absolute value of between 2 and 7 volts, and the second phase may have a second phase amplitude with an absolute value of between 2 and 7 volts.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the first phase may have a first phase amplitude with an absolute value of between 1 and 4 volts, and the second phase may have a second phase amplitude with an absolute value of between 1 and 4 volts.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the second phase may have a duration of less than 60 microseconds.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the second phase may have a duration of less than 30 microseconds.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the second phase may have a duration of less than 20 microseconds.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the first phase may have a duration of between forty percent and sixty percent of the duration of the second phase.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the first phase and the second phase may each be a substantially rectangular pulse.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the first phase and the second phase may each be substantially a rectangular pulse, a saw tooth pulse, an exponential pulse, a trapezoid pulse, or a stepped pulse.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the phasic conducted communication pulse may comprise a third phase.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the third phase may have the first polarity.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the phasic conducted communication pulse may be substantially charge balanced.

Additionally, or alternatively, in any of the above embodiments with respect to the first illustrative embodiment, the phasic conducted communication pulse may have four or more phases.

In a second illustrative embodiment, a medical device may comprise a housing, a pulse generation circuit disposed at least partially within the housing, a plurality of electrodes electrically coupled to the pulse generation circuit, the plurality of electrodes being exposed externally to the housing, and a controller operatively coupled to the pulse generation circuit. In some instances, the controller may be configured to command the pulse generation circuit to deliver a phasic conducted communication pulse via at least two of the plurality of electrodes. Additionally, in some cases, the phasic conducted communication pulse may comprise at least three phases.

Additionally, or alternatively, with respect to the second illustrative embodiment, the phasic conducted communication pulse may comprise a first phase, a second phase, and a third phase, with each phase having a duration and an amplitude, and wherein the first phase and the third phase may have a first polarity and the second phase may have a second opposite polarity.

Additionally, or alternatively, in any of the above embodiments with respect to the second illustrative embodiment, the duration of the second phase may be less than 60 microseconds.

Additionally, or alternatively, in any of the above embodiments with respect to the second illustrative embodiment, the duration of the first phase of the phasic conducted communication pulse may be between five percent and eighty percent of the duration of the second phase of the phasic conducted communication pulse.

Additionally, or alternatively, in any of the above embodiments with respect to the second illustrative embodiment, the duration of the second phase may be less than 50 microseconds, and the duration of the first phase may be between forty percent and sixty percent of the duration of the second phase.

Additionally, or alternatively, in any of the above embodiments with respect to the second illustrative embodiment, the phasic conducted communication pulse may be substantially charge balanced.

Additionally, or alternatively, in any of the above embodiments with respect to the second illustrative embodiment, the phasic conducted communication pulse may have four or more phases, each of the four or more phases having a duration.

In a third illustrative embodiment, a medical device may comprise a housing, a plurality of electrodes coupled to the housing, and a communication circuit electrically connected to the plurality of electrodes. In at least some instances, the communication circuit may be configured to deliver a phasic conducted communication pulse via two or more of the plurality of electrodes for communicating information external to the medical device. In at least some cases, the phasic conducted communication pulse may comprises a first phase, followed by a second phase, followed by a third phase, where the first phase and the third phase have a first polarity, and the second phase has an opposite second polarity.

Additionally, or alternatively, with respect to the third illustrative embodiment, the second phase may have a duration of less than 60 microseconds, and the first phase may have a duration of between five percent and eighty percent of the duration of the second phase.

The above summary is not intended to describe each embodiment or every implementation of the present disclosure. Advantages and attainments, together with a more complete understanding of the disclosure, will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of an illustrative leadless cardiac pacemaker (LCP) according to one example embodiment of the present disclosure;

FIG. 2 is a schematic block diagram of another illustrative medical device that may be used in conjunction with the LCP of FIG. 1;

FIG. 3 is a schematic diagram of an illustrative medical system that includes multiple LCPs and/or other devices in communication with one another;

FIG. 4 is a schematic diagram of a system including an LCP and another medical device, in accordance with another embodiment of the present disclosure;

FIGS. 5A-5B depict illustrative biphasic conducted communication pulses with rectangular phase morphologies;

FIG. 6A depicts an illustrative biphasic conducted communication pulse width a saw-tooth phase morphology;

FIG. 6B depicts an illustrative biphasic conducted communication pulse width an exponential phase morphology;

FIG. 6C depicts an illustrative biphasic conducted communication pulse width a trapezoid phase morphology;

FIG. 6D depicts an illustrative biphasic conducted communication pulse width a stepped phase morphology;

FIG. 7 depicts a communication pulse sequence demonstrating one illustrative information encoding scheme;

FIG. 8 depicts another communication pulse sequence demonstrating another illustrative information encoding scheme;

FIGS. 9A-9B depict illustrative tri-phasic conducted communication pulses;

FIGS. 10A-10B depict illustrative quad-phasic conducted communication pulses;

FIGS. 11A-11B depict illustrative hexa-phasic conducted communication pulses; and

FIG. 12 shows a graph of data collected from a canine showing the heart capture threshold versus pulse width duration for various different pulse morphologies.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of embodiment in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure.

The present disclosure relates to systems, devices, and methods for communicating with or between implantable medical devices such as heart stimulating devices, neuro-stimulators, diagnostic devices, chemical sensors, pressure sensors, temperature sensors, etc. Merely for convenience, many of the examples described herein are directed at heart stimulating devices such as implantable pacemakers and/or implantable cardioverter-defibrillators. The intention is not to limit the disclosure to implantable pacemakers and/or implantable cardioverter-defibrillators. Rather, the intention is to cover communication with or between any suitable implantable medical device.

FIG. 1 is a conceptual schematic block diagram of an illustrative leadless cardiac pacemaker (LCP) that may be implanted on the heart or within a chamber of the heart and may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to the heart of the patient. Example electrical stimulation therapy may include bradycardia pacing, rate responsive pacing therapy, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) therapy and/or the like. As can be seen in FIG. 1, LCP 100 may be a compact device with all components housed within LCP 100 or directly on housing 120. In some instances, LCP 100 may include communication module 102, pulse generator module 104, electrical sensing module 106, mechanical sensing module 108, processing module 110, energy storage module 112, and electrodes 114.

As depicted in FIG. 1, LCP 100 may include electrodes 114, which can be secured relative to housing 120 and electrically exposed to tissue and/or blood surrounding LCP 100. Electrodes 114 may generally conduct electrical signals to and from LCP 100 and the surrounding tissue and/or blood. Such electrical signals can include communication signals, electrical stimulation pulses, and intrinsic cardiac electrical signals, to name a few. Intrinsic cardiac electrical signals may include electrical signals generated by the heart and may be represented by an electrocardiogram (ECG).

Electrodes 114 may include one or more biocompatible conductive materials such as various metals or alloys that are known to be safe for implantation within a human body. In some instances, electrodes 114 may be generally disposed on either end of LCP 100 and may be in electrical communication with one or more of modules 102, 104, 106, 108, and 110. In embodiments where electrodes 114 are secured directly to housing 120, an insulative material may electrically isolate the electrodes 114 from adjacent electrodes, housing 120, and/or other parts of LCP 100. In some instances, some or all of electrodes 114 may be spaced from housing 120 and connected to housing 120 and/or other components of LCP 100 through connecting wires. In such instances, the electrodes 114 may be placed on a tail (not shown) that extends out away from the housing 120. As shown in FIG. 1, in some embodiments, LCP 100 may include electrodes 114′. Electrodes 114′ may be in addition to electrodes 114, or may replace one or more of electrodes 114. Electrodes 114′ may be similar to electrodes 114 except that electrodes 114′ are disposed on the sides of LCP 100. In some cases, electrodes 114′ may increase the number of electrodes by which LCP 100 may deliver communication signals and/or electrical stimulation pulses, and/or may sense intrinsic cardiac electrical signals, communication signals, and/or electrical stimulation pulses.

Electrodes 114 and/or 114′ may assume any of a variety of sizes and/or shapes, and may be spaced at any of a variety of spacings. For example, electrodes 114 may have an outer diameter of two to twenty millimeters (mm). In other embodiments, electrodes 114 and/or 114′ may have a diameter of two, three, five, seven millimeters (mm), or any other suitable diameter, dimension and/or shape. Example lengths for electrodes 114 and/or 114′ may include, for example, one, three, five, ten millimeters (mm), or any other suitable length. As used herein, the length is a dimension of electrodes 114 and/or 114′ that extends away from the outer surface of the housing 120. In some instances, at least some of electrodes 114 and/or 114′ may be spaced from one another by a distance of twenty, thirty, forty, fifty millimeters (mm), or any other suitable spacing. The electrodes 114 and/or 114′ of a single device may have different sizes with respect to each other, and the spacing and/or lengths of the electrodes on the device may or may not be uniform.

In the embodiment shown, communication module 102 may be electrically coupled to electrodes 114 and/or 114′ and may be configured to deliver communication pulses to tissues of the patient for communicating with other devices such as sensors, programmers, other medical devices, and/or the like. Communication signals, as used herein, may be any modulated signal that conveys information to another device, either by itself or in conjunction with one or more other modulated signals. In some embodiments, communication signals may be limited to sub-threshold signals that do not result in capture of the heart yet still convey information. The communication signals may be delivered to another device that is located either external or internal to the patient's body. In some instances, the communication may take the form of distinct communication pulses separated by various amounts of time. In some of these cases, the timing between successive pulses may convey information. Communication module 102 may additionally be configured to sense for communication signals delivered by other devices, which may be located external or internal to the patient's body.

Communication module 102 may communicate to help accomplish one or more desired functions. Some example functions include delivering sensed data, using communicated data for determining occurrences of events such as arrhythmias, coordinating delivery of electrical stimulation therapy, and/or other functions. In some cases, LCP 100 may use communication signals to communicate raw information, processed information, messages and/or commands, and/or other data. Raw information may include information such as sensed electrical signals (e.g. a sensed ECG), signals gathered from coupled sensors, and the like. In some embodiments, the processed information may include signals that have been filtered using one or more signal processing techniques. Processed information may also include parameters and/or events that are determined by the LCP 100 and/or another device, such as a determined heart rate, timing of determined heartbeats, timing of other determined events, determinations of threshold crossings, expirations of monitored time periods, accelerometer signals, activity level parameters, blood-oxygen parameters, blood pressure parameters, heart sound parameters, and the like. Messages and/or commands may include instructions or the like directing another device to take action, notifications of imminent actions of the sending device, requests for reading from the receiving device, requests for writing data to the receiving device, information messages, and/or other messages commands.

In at least some embodiments, communication module 102 (or LCP 100) may further include switching circuitry to selectively connect one or more of electrodes 114 and/or 114′ to communication module 102 in order to select which electrodes 114 and/or 114′ that communication module 102 delivers communication pulses. It is contemplated that communication module 102 may be communicating with other devices via conducted signals, radio frequency (RF) signals, optical signals, acoustic signals, inductive coupling, and/or any other suitable communication methodology. Where communication module 102 generates electrical communication signals, communication module 102 may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering communication signals. In the embodiment shown, communication module 102 may use energy stored in energy storage module 112 to generate the communication signals. In at least some examples, communication module 102 may include a switching circuit that is connected to energy storage module 112 and, with the switching circuitry, may connect energy storage module 112 to one or more of electrodes 114/114′ to generate the communication signals.

As shown in FIG. 1, a pulse generator module 104 may be electrically connected to one or more of electrodes 114 and/or 114′. Pulse generator module 104 may be configured to generate electrical stimulation pulses and deliver the electrical stimulation pulses to tissues of a patient via one or more of the electrodes 114 and/or 114′ in order to effectuate one or more electrical stimulation therapies. Electrical stimulation pulses as used herein are meant to encompass any electrical signals that may be delivered to tissue of a patient for purposes of treatment of any type of disease or abnormality. For example, when used to treat heart disease, the pulse generator module 104 may generate electrical stimulation pacing pulses for capturing the heart of the patient, i.e. causing the heart to contract in response to the delivered electrical stimulation pulse. In some of these cases, LCP 100 may vary the rate at which pulse generator module 104 generates the electrical stimulation pulses, for example in rate adaptive pacing. In other embodiments, the electrical stimulation pulses may include defibrillation/cardioversion pulses for shocking the heart out of fibrillation or into a normal heart rhythm. In yet other embodiments, the electrical stimulation pulses may include anti-tachycardia pacing (ATP) pulses. It should be understood that these are just some examples. When used to treat other ailments, the pulse generator module 104 may generate electrical stimulation pulses suitable for neurostimulation therapy or the like. Pulse generator module 104 may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering appropriate electrical stimulation pulses. In at least some embodiments, pulse generator module 104 may use energy stored in energy storage module 112 to generate the electrical stimulation pulses. In some particular embodiments, pulse generator module 104 may include a switching circuit that is connected to energy storage module 112 and may connect energy storage module 112 to one or more of electrodes 114/114′ to generate electrical stimulation pulses.

LCP 100 may further include an electrical sensing module 106 and mechanical sensing module 108. Electrical sensing module 106 may be configured to sense intrinsic cardiac electrical signals conducted from electrodes 114 and/or 114′ to electrical sensing module 106. For example, electrical sensing module 106 may be electrically connected to one or more electrodes 114 and/or 114′ and electrical sensing module 106 may be configured to receive cardiac electrical signals conducted through electrodes 114 and/or 114′ via a sensor amplifier or the like. In some embodiments, the cardiac electrical signals may represent local information from the chamber in which LCP 100 is implanted. For instance, if LCP 100 is implanted within a ventricle of the heart, cardiac electrical signals sensed by LCP 100 through electrodes 114 and/or 114′ may represent ventricular cardiac electrical signals. Mechanical sensing module 108 may include, or be electrically connected to, various sensors, such as accelerometers, including multi-axis accelerometers such as two- or three-axis accelerometers, gyroscopes, including multi-axis gyroscopes such as two- or three-axis gyroscopes, blood pressure sensors, heart sound sensors, piezoelectric sensors, blood-oxygen sensors, and/or other sensors which measure one or more physiological parameters of the heart and/or patient. Mechanical sensing module 108, when present, may gather signals from the sensors indicative of the various physiological parameters. Both electrical sensing module 106 and mechanical sensing module 108 may be connected to processing module 110 and may provide signals representative of the sensed cardiac electrical signals and/or physiological signals to processing module 110. Although described with respect to FIG. 1 as separate sensing modules, in some embodiments, electrical sensing module 106 and mechanical sensing module 108 may be combined into a single module. In at least some examples, LCP 100 may only include one of electrical sensing module 106 and mechanical sensing module 108. In some cases, any combination of the processing module 110, electrical sensing module 106, mechanical sensing module 108, communication module 102, pulse generator module 104 and/or energy storage module may be considered a controller of the LCP 100.

Processing module 110 may be configured to direct the operation of LCP 100 and may, in some embodiments, be termed a controller. For example, processing module 110 may be configured to receive cardiac electrical signals from electrical sensing module 106 and/or physiological signals from mechanical sensing module 108. Based on the received signals, processing module 110 may determine, for example, occurrences and types of arrhythmias and other determinations such as whether LCP 100 has become dislodged. Processing module 110 may further receive information from communication module 102. In some embodiments, processing module 110 may additionally use such received information to determine occurrences and types of arrhythmias and/or and other determinations such as whether LCP 100 has become dislodged. In still some additional embodiments, LCP 100 may use the received information instead of the signals received from electrical sensing module 106 and/or mechanical sensing module 108—for instance if the received information is deemed to be more accurate than the signals received from electrical sensing module 106 and/or mechanical sensing module 108 or if electrical sensing module 106 and/or mechanical sensing module 108 have been disabled or omitted from LCP 100.

After determining an occurrence of an arrhythmia, processing module 110 may control pulse generator module 104 to generate electrical stimulation pulses in accordance with one or more electrical stimulation therapies to treat the determined arrhythmia. For example, processing module 110 may control pulse generator module 104 to generate pacing pulses with varying parameters and in different sequences to effectuate one or more electrical stimulation therapies. As one example, in controlling pulse generator module 104 to deliver bradycardia pacing therapy, processing module 110 may control pulse generator module 104 to deliver pacing pulses designed to capture the heart of the patient at a regular interval to help prevent the heart of a patient from falling below a predetermined threshold. In some cases, the rate of pacing may be increased with an increased activity level of the patient (e.g. rate adaptive pacing). For instance, processing module 110 may monitor one or more physiological parameters of the patient which may indicate a need for an increased heart rate (e.g. due to increased metabolic demand). Processing module 110 may then increase the rate at which pulse generator module 104 generates electrical stimulation pulses. Adjusting the rate of delivery of the electrical stimulation pulses based on the one or more physiological parameters may extend the battery life of LCP 100 by only requiring higher rates of delivery of electrical stimulation pulses when the physiological parameters indicate there is a need for increased cardiac output. Additionally, adjusting the rate of delivery of the electrical stimulation pulses may increase a comfort level of the patient by more closely matching the rate of delivery of electrical stimulation pulses with the cardiac output need of the patient.

For ATP therapy, processing module 110 may control pulse generator module 104 to deliver pacing pulses at a rate faster than an intrinsic heart rate of a patient in attempt to force the heart to beat in response to the delivered pacing pulses rather than in response to intrinsic cardiac electrical signals. Once the heart is following the pacing pulses, processing module 110 may control pulse generator module 104 to reduce the rate of delivered pacing pulses down to a safer level. In CRT, processing module 110 may control pulse generator module 104 to deliver pacing pulses in coordination with another device to cause the heart to contract more efficiently. In cases where pulse generator module 104 is capable of generating defibrillation and/or cardioversion pulses for defibrillation/cardioversion therapy, processing module 110 may control pulse generator module 104 to generate such defibrillation and/or cardioversion pulses. In some cases, processing module 110 may control pulse generator module 104 to generate electrical stimulation pulses to provide electrical stimulation therapies different than those examples described above.

Aside from controlling pulse generator module 104 to generate different types of electrical stimulation pulses and in different sequences, in some embodiments, processing module 110 may also control pulse generator module 104 to generate the various electrical stimulation pulses with varying pulse parameters. For example, each electrical stimulation pulse may have a pulse width and a pulse amplitude. Processing module 110 may control pulse generator module 104 to generate the various electrical stimulation pulses with specific pulse widths and pulse amplitudes. For example, processing module 110 may cause pulse generator module 104 to adjust the pulse width and/or the pulse amplitude of electrical stimulation pulses if the electrical stimulation pulses are not effectively capturing the heart. Such control of the specific parameters of the various electrical stimulation pulses may help LCP 100 provide more effective delivery of electrical stimulation therapy.

In some embodiments, processing module 110 may further control communication module 102 to send information to other devices. For example, processing module 110 may control communication module 102 to generate one or more communication signals for communicating with other devices of a system of devices. For instance, processing module 110 may control communication module 102 to generate communication signals in particular pulse sequences, where the specific sequences convey different information. Communication module 102 may also receive communication signals for potential action by processing module 110.

In further embodiments, processing module 110 may control switching circuitry by which communication module 102 and pulse generator module 104 deliver communication signals and/or electrical stimulation pulses to tissue of the patient. As described above, both communication module 102 and pulse generator module 104 may include circuitry for connecting one or more electrodes 114 and/or 114′ to communication module 102 and/or pulse generator module 104 so those modules may deliver the communication signals and electrical stimulation pulses to tissue of the patient. The specific combination of one or more electrodes by which communication module 102 and/or pulse generator module 104 deliver communication signals and electrical stimulation pulses may influence the reception of communication signals and/or the effectiveness of electrical stimulation pulses. Although it was described that each of communication module 102 and pulse generator module 104 may include switching circuitry, in some embodiments, LCP 100 may have a single switching module connected to the communication module 102, the pulse generator module 104, and electrodes 114 and/or 114′. In such embodiments, processing module 110 may control the switching module to connect modules 102/104 and electrodes 114/114′ as appropriate.

In some embodiments, processing module 110 may include a pre-programmed chip, such as a very-large-scale integration (VLSI) chip or an application specific integrated circuit (ASIC). In such embodiments, the chip may be pre-programmed with control logic in order to control the operation of LCP 100. By using a pre-programmed chip, processing module 110 may use less power than other programmable circuits while able to maintain basic functionality, thereby potentially increasing the battery life of LCP 100. In other instances, processing module 110 may include a programmable microprocessor or the like. Such a programmable microprocessor may allow a user to adjust the control logic of LCP 100 after manufacture, thereby allowing for greater flexibility of LCP 100 than when using a pre-programmed chip. In still other embodiments, processing module 110 may not be a single component. For example, processing module 110 may include multiple components positioned at disparate locations within LCP 100 in order to perform the various described functions. For example, certain functions may be performed in one component of processing module 110, while other functions are performed in a separate component of processing module 110.

Processing module 110, in additional embodiments, may include a memory circuit and processing module 110 may store information on and read information from the memory circuit. In other embodiments, LCP 100 may include a separate memory circuit (not shown) that is in communication with processing module 110, such that processing module 110 may read and write information to and from the separate memory circuit. The memory circuit, whether part of processing module 110 or separate from processing module 110, may be volatile memory, non-volatile memory, or a combination of volatile memory and non-volatile memory.

Energy storage module 112 may provide a power source to LCP 100 for its operations. In some embodiments, energy storage module 112 may be a non-rechargeable lithium-based battery. In other embodiments, the non-rechargeable battery may be made from other suitable materials. In some embodiments, energy storage module 112 may include a rechargeable battery. In still other embodiments, energy storage module 112 may include other types of energy storage devices such as capacitors or super capacitors.

To implant LCP 100 inside a patient's body, an operator (e.g., a physician, clinician, etc.), may fix LCP 100 to the cardiac tissue of the patient's heart. To facilitate fixation, LCP 100 may include one or more anchors 116. The one or more anchors 116 are shown schematically in FIG. 1. The one or more anchors 116 may include any number of fixation or anchoring mechanisms. For example, one or more anchors 116 may include one or more pins, staples, threads, screws, helix, tines, and/or the like. In some embodiments, although not shown, one or more anchors 116 may include threads on its external surface that may run along at least a partial length of an anchor member. The threads may provide friction between the cardiac tissue and the anchor to help fix the anchor member within the cardiac tissue. In some cases, the one or more anchors 116 may include an anchor member that has a cork-screw shape that can be screwed into the cardiac tissue. In other embodiments, anchor 116 may include other structures such as barbs, spikes, or the like to facilitate engagement with the surrounding cardiac tissue.

In some examples, LCP 100 may be configured to be implanted on a patient's heart or within a chamber of the patient's heart. For instance, LCP 100 may be implanted within any of a left atrium, right atrium, left ventricle, or right ventricle of a patient's heart. By being implanted within a specific chamber, LCP 100 may be able to sense cardiac electrical signals originating or emanating from the specific chamber that other devices may not be able to sense with such resolution. Where LCP 100 is configured to be implanted on a patient's heart, LCP 100 may be configured to be implanted on or adjacent to one of the chambers of the heart, or on or adjacent to a path along which intrinsically generated cardiac electrical signals generally follow. In these examples, LCP 100 may also have an enhanced ability to sense localized intrinsic cardiac electrical signals and deliver localized electrical stimulation therapy. In embodiments where LCP 100 includes an accelerometer, LCP 100 may additionally be able to sense the motion of the cardiac wall to which LCP 100 is attached.

FIG. 2 depicts an embodiment of another device, medical device (MD) 200, which may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to tissues of the patient. In the embodiment shown, MD 200 may include a communication module 202, a pulse generator module 204, an electrical sensing module 206, a mechanical sensing module 208, a processing module 210, and an energy storage module 218. Each of modules 202, 204, 206, 208, and 210 may be similar to modules 102, 104, 106, 108, and 110 of LCP 100. Additionally, energy storage module 218 may be similar to energy storage module 112 of LCP 100. However, in some embodiments, MD 200 may have a larger volume within housing 220. In such embodiments, MD 200 may include a larger energy storage module 218 and/or a larger processing module 210 capable of handling more complex operations than processing module 110 of LCP 100.

While MD 200 may be another leadless device such as shown in FIG. 1, in some instances MD 200 may include leads, such as leads 212. Leads 212 may include electrical wires that conduct electrical signals between electrodes 214 and one or more modules located within housing 220. In some cases, leads 212 may be connected to and extend away from housing 220 of MD 200. In some embodiments, leads 212 are implanted on, within, or adjacent to a heart of a patient. Leads 212 may contain one or more electrodes 214 positioned at various locations on leads 212 and various distances from housing 220. Some leads 212 may only include a single electrode 214, while other leads 212 may include multiple electrodes 214. Generally, electrodes 214 are positioned on leads 212 such that when leads 212 are implanted within the patient, one or more of the electrodes 214 are positioned to perform a desired function. In some cases, the one or more of the electrodes 214 may be in contact with the patient's cardiac tissue. In other cases, the one or more of the electrodes 214 may be positioned subcutaneously but adjacent the patient's heart. The electrodes 214 may conduct intrinsically generated electrical cardiac signals to leads 212. Leads 212 may, in turn, conduct the received electrical cardiac signals to one or more of the modules 202, 204, 206, and 208 of MD 200. In some cases, MD 200 may generate electrical stimulation signals, and leads 212 may conduct the generated electrical stimulation signals to electrodes 214. Electrodes 214 may then conduct the electrical stimulation signals to the cardiac tissue of the patient (either directly or indirectly). MD 200 may also include one or more electrodes 214 not disposed on a lead 212. For example, one or more electrodes 214 may be connected directly to housing 220.

Leads 212, in some embodiments, may additionally contain one or more sensors, such as accelerometers, blood pressure sensors, heart sound sensors, blood-oxygen sensors, and/or other sensors which are configured to measure one or more physiological parameters of the heart and/or patient. In such embodiments, mechanical sensing module 208 may be in electrical communication with leads 212 and may receive signals generated from such sensors.

While not required, in some embodiments MD 200 may be an implantable medical device. In such embodiments, housing 220 of MD 200 may be implanted in, for example, a transthoracic region of the patient. Housing 220 may generally include any of a number of known materials that are safe for implantation in a human body and may, when implanted, hermetically seal the various components of MD 200 from fluids and tissues of the patient's body. In such embodiments, leads 212 may be implanted at one or more various locations within the patient, such as within the heart of the patient, adjacent to the heart of the patient, adjacent to the spine of the patient, or any other desired location.

In some embodiments, MD 200 may be an implantable cardiac pacemaker (ICP). In these embodiments, MD 200 may have one or more leads, for example leads 212, which are implanted on or within the patient's heart. The one or more leads 212 may include one or more electrodes 214 that are in contact with cardiac tissue and/or blood of the patient's heart. MD 200 may be configured to sense intrinsically generated cardiac electrical signals and determine, for example, one or more cardiac arrhythmias based on analysis of the sensed signals. MD 200 may be configured to deliver CRT, ATP therapy, bradycardia therapy, and/or other therapy types via leads 212 implanted within the heart. In some embodiments, MD 200 may additionally be configured to provide defibrillation/cardioversion therapy.

In some instances, MD 200 may be an implantable cardioverter-defibrillator (ICD). In such embodiments, MD 200 may include one or more leads implanted within a patient's heart. MD 200 may also be configured to sense electrical cardiac signals, determine occurrences of tachyarrhythmias based on the sensed electrical cardiac signals, and deliver defibrillation and/or cardioversion therapy in response to determining an occurrence of a tachyarrhythmia (for example by delivering defibrillation and/or cardioversion pulses to the heart of the patient). In other embodiments, MD 200 may be a subcutaneous implantable cardioverter-defibrillator (SICD). In embodiments where MD 200 is an SICD, one of leads 212 may be a subcutaneously implanted lead. In at least some embodiments where MD 200 is an SICD, MD 200 may include only a single lead which is implanted subcutaneously but outside of the chest cavity, however this is not required.

In some embodiments, MD 200 may not be an implantable medical device. Rather, MD 200 may be a device external to the patient's body, and electrodes 214 may be skin-electrodes that are placed on a patient's body. In such embodiments, MD 200 may be able to sense surface electrical signals (e.g. electrical cardiac signals that are generated by the heart or electrical signals generated by a device implanted within a patient's body and conducted through the body to the skin). MD 200 may further be configured to deliver various types of electrical stimulation therapy, including, for example, defibrillation therapy via skin-electrodes 214.

FIG. 3 illustrates an embodiment of a medical device system and a communication pathway through which multiple medical devices 302, 304, 306, and/or 310 of the medical device system may communicate. In the embodiment shown, medical device system 300 may include LCPs 302 and 304, external medical device 306, and other sensors/devices 310. External device 306 may be a device disposed external to a patient's body, as described previously with respect to MD 200. In at least some examples, external device 306 may represent an external support device such as a device programmer, as will be described in more detail below. Other sensors/devices 310 may be any of the devices described previously with respect to MD 200, such as ICPs, ICDs, and SICDs. Other sensors/devices 310 may also include various diagnostic sensors that gather information about the patient, such as accelerometers, blood pressure sensors, or the like. In some cases, other sensors/devices 310 may include an external programmer device that may be used to program one or more devices of system 300.

Various devices of system 300 may communicate via communication pathway 308. For example, LCPs 302 and/or 304 may sense intrinsic cardiac electrical signals and may communicate such signals to one or more other devices 302/304, 306, and 310 of system 300 via communication pathway 308. In one embodiment, one or more of devices 302/304 may receive such signals and, based on the received signals, determine an occurrence of an arrhythmia. In some cases, device or devices 302/304 may communicate such determinations to one or more other devices 306 and 310 of system 300. In some cases, one or more of devices 302/304, 306, and 310 of system 300 may take action based on the communicated determination of an arrhythmia, such as by delivering a suitable electrical stimulation to the heart of the patient. One or more of devices 302/304, 306, and 310 of system 300 may additionally communicate command or response messages via communication pathway 308. The command messages may cause a receiving device to take a particular action whereas response messages may include requested information or a confirmation that a receiving device did, in fact, receive a communicated message or data.

It is contemplated that the various devices of system 300 may communicate via pathway 308 using RF signals, inductive coupling, optical signals, acoustic signals, or any other signals suitable for communication. Additionally, in at least some embodiments, the various devices of system 300 may communicate via pathway 308 using multiple signal types. For instance, other sensors/device 310 may communicate with external device 306 using a first signal type (e.g. RF communication) but communicate with LCPs 302/304 using a second signal type (e.g. conducted communication). Further, in some embodiments, communication between devices may be limited. For instance, as described above, in some embodiments, LCPs 302/304 may communicate with external device 306 only through other sensors/devices 310, where LCPs 302/304 send signals to other sensors/devices 310, and other sensors/devices 310 relay the received signals to external device 306.

In some cases, the various devices of system 300 may communicate via pathway 308 using conducted communication signals. Accordingly, devices of system 300 may have components that allow for such conducted communication. For instance, the devices of system 300 may be configured to transmit conducted communication signals (e.g. a voltage and/or current waveform punctuated with current and/or voltage pulses, referred herein as electrical communication pulses) into the patient's body via one or more electrodes of a transmitting device, and may receive the conducted communication signals via one or more electrodes of a receiving device. The patient's body may “conduct” the conducted communication signals from the one or more electrodes of the transmitting device to the electrodes of the receiving device in the system 300. In such embodiments, the delivered conducted communication signals may differ from pacing pulses, defibrillation and/or cardioversion pulses, or other electrical stimulation therapy signals. For example, the devices of system 300 may deliver electrical communication pulses at an amplitude/pulse width that is sub-threshold. That is, the communication pulses have an amplitude/pulse width designed to not capture the heart. In some cases, the amplitude/pulse width of the delivered electrical communication pulses may be above the capture threshold of the heart, but may be delivered during a refractory period of the heart and/or may be incorporated in or modulated onto a pacing pulse, if desired.

Additionally, unlike normal electrical stimulation therapy pulses, the electrical communication pulses may be delivered in specific sequences which convey information to receiving devices. For instance, delivered electrical communication pulses may be modulated in any suitable manner to encode communicated information. In some cases, the communication pulses may be pulse width modulated and/or amplitude modulated. Alternatively, or in addition, the time between pulses may be modulated to encode desired information. In some cases, a predefined sequence of communication pulses may represent a corresponding symbol (e.g. a logic “1” symbol, a logic “0” symbol, an ATP therapy trigger symbol, etc.). In some cases, conducted communication pulses may be voltage pulses, current pulses, bi-phasic voltage pulses, bi-phasic current pulses, tri-phasic voltage pulses, tri-phasic current pulses, quad-phasic voltage pulses, quad-phasic current pulses, hex-phasic voltage pulses, hex-phasic current pulses, or any other suitable electrical pulse as desired, as further detailed herein.

FIG. 4 depicts an illustrative medical device system 400 that may be configured to operate together. For example, system 400 may include multiple devices that are implanted within a patient and are configured to sense physiological signals, determine occurrences of cardiac arrhythmias, and deliver electrical stimulation to treat detected cardiac arrhythmias. In some embodiments, the devices of system 400 may be configured to determine occurrences of dislodgment of one or more devices of system 400. In FIG. 4, an LCP 402 is shown fixed to the interior of the right ventricle of the heart 410, and a pulse generator 406 is shown coupled to a lead 412 having one or more electrodes 408 a-408 c. In some cases, pulse generator 406 may be part of a subcutaneous implantable cardioverter-defibrillator (SICD), and the one or more electrodes 408 a-408 c may be positioned subcutaneously adjacent the heart. LCP 402 may communicate with the SICD, such as via communication pathway 308. The locations of LCP 402, pulse generator 406, lead 412, and electrodes 408 a-c depicted in FIG. 4 are just illustrative. In other embodiments of system 400, LCP 402 may be positioned in the left ventricle, right atrium, or left atrium of the heart, as desired. In still other embodiments, LCP 402 may be implanted externally adjacent to heart 410 or even remote from heart 410.

Medical device system 400 may also include external support device 420. External support device 420 can be used to perform functions such as device identification, device programming and/or transfer of real-time and/or stored data between devices using one or more of the communication techniques described herein, or other functions involving communication with one or more devices of system 400. As one example, communication between external support device 420 and pulse generator 406 can be performed via a wireless mode, and communication between pulse generator 406 and LCP 402 can be performed via a conducted communication mode. In some embodiments, communication between LCP 402 and external support device 420 is accomplished by sending communication information through pulse generator 406. However, in other embodiments, communication between the LCP 402 and external support device 420 may be via a communication module.

FIG. 4 only illustrates one example embodiment of a medical device system that may be configured to operate according to techniques disclosed herein. Other example medical device systems may include additional or different medical devices and/or configurations. For instance, other medical device systems that are suitable to operate according to techniques disclosed herein may include additional LCPs implanted within the heart. Another example medical device system may include a plurality of LCPs with or without other devices such as pulse generator 406, with at least one LCP capable of delivering defibrillation therapy. Still another example may include one or more LCPs implanted along with a transvenous pacemaker and with or without an implanted SICD. In yet other embodiments, the configuration or placement of the medical devices, leads, and/or electrodes may be different from those depicted in FIG. 4. Accordingly, it should be recognized that numerous other medical device systems, different from system 400 depicted in FIG. 4, may be operated in accordance with techniques disclosed herein. As such, the embodiment shown in FIG. 4 should not be viewed as limiting in any way.

FIGS. 5A-B, 6A-6D, 9A-B, 10A-10B and 11A-11B depict example phasic communication pulses that may be used according to techniques of the present disclosure. Generally, these phasic conducted communication pulses intentionally differ from pacing pulses or other electrical stimulation therapy signals. The described phasic conducted communication pulses may have an amplitude/pulse width combination that is intentionally sub-threshold so as to not capture body tissue such as the heart. FIGS. 7-8 describe illustrative communication schemes suitable for convey information between devices using the illustrative phasic conducted communication pulses shown in FIGS. 5A-B, 6A-6D, 9A-B, 10A-10B and 11A-11B.

Generally, the phasic conducted communication pulses described herein may be either voltage pulses or current pulses. In a voltage pulse, the voltage amplitude is controlled and the current is dependent on the voltage amplitude and the resistance of the transmission medium. In a current pulse, the current amplitude is controlled and the voltage is dependent on the current amplitude and the resistance of the transmission medium. In some examples, the phasic conducted communication pulses may be combinations of voltage pulses and current pulses (e.g. some of the phases include a voltage pulse while other phases include a current pulse). It is contemplated that any of the devices described with respect to FIGS. 1-4 may include circuitry that generates such phasic conducted communication pulses.

FIGS. 5A-B depict first examples of phasic conducted communication pulses, including phasic conducted communication pulses 501, 503. As shown in FIGS. 5A-B, phasic conducted communication pulses 501, 503 may each include first phases 505 a, 505 b and second phases 507 a, 507 b. In these embodiments, each of first phases 505 a, 505 b may have a first polarity and each of second phases 507 a, 507 b may have a second polarity, with the first polarity and the second polarity being opposite. Example phasic conducted communication pulse 501 is depicted with first phase 505 a having a positive polarity while second phase 507 a has a negative polarity, while phasic conducted communication pulse 503 is depicted in an opposite manner.

First phases 505 a, 505 b may have amplitudes 506 a, 506 b and abbreviated pulse widths 502 a, 502 b. Second phases 507 a, 507 b may have amplitudes 508 a, 508 b and un-abbreviated pulse widths 504 a, 504 b. In these embodiments, pulse widths 502 a, 502 b of the first phases 505 a, 505 b may be considered ‘abbreviate pulse widths’ because their length are shown to be less than the length of pulse widths 504 a, 504 b of the second phases 507 a, 507 b. For example, abbreviated pulse widths 502 a, 502 b of the first phases 505 a, 505 b may have values that range between about five percent and about eighty percent of the value of un-abbreviated pulse widths 504 a, 504 b of the second phases 507 a, 507 b. The term “about” means±10% of the specified value.

In some embodiments, pulse widths 504 a, 504 b of the second phases 507 a, 507 b may have values that range between about one microseconds and about seventy-five microseconds. In more specific embodiments, pulse widths 504 a, 504 b may have values that range between about one microseconds and about thirty microseconds, or may be about five microseconds, about ten microseconds, about fifteen microseconds, about twenty microseconds, about twenty-five microseconds, about thirty microseconds, about thirty-five microseconds, about forty microseconds, or any other suitable value. For a voltage pulse, the pulse width is the interval of time between the two times the voltage crosses 50% of the amplitude of the voltage pulse. For a current pulse, the pulse width is the interval of time between the two times the current crosses 50% of the amplitude of the current pulse.

Abbreviated pulse widths 502 a, 502 b may have values that range between about five percent and about eighty percent of the value of pulse widths 504 a, 504 b. In more specific embodiments, abbreviated pulse widths 502 a, 502 b may have values that range between about ten percent and about fifty percent of the value of pulse widths 504 a, 504 b, or be about ten percent, about twenty percent, about twenty-five percent, about thirty percent, about forty percent, about fifty percent, or any other suitable percentage of the value of pulse widths 504 a, 504 b.

In some cases, pulse widths 504 a and 504 b (or abbreviated pulse widths 502 a and 502 b), themselves, may not have exactly the same values. For instance, the values of pulse widths 504 a, 504 b (or abbreviated pulse widths 502 a, 502 b) may vary between successively delivered phasic conducted communication pulses. In some cases the values that differ between successively delivered phasic conducted communication pulses may vary by less than about ten percent.

In some instances, amplitudes 506 a, 506 b, 508 a, and 508 b may all be equal or about equal with amplitudes 508 a, 508 b having polarities (e.g. positive magnitude or negative magnitude relative to neutral or ground) opposite of amplitudes 506 a, 506 b. In general, amplitudes 506 a, 506 b, 508 a, and 508 b may be any suitable value, but in some specific embodiments, amplitudes 506 a, 506 b, 508 a, and 508 b may have values that range between about one volt and about fifteen volts. In further embodiments, amplitudes 506 a, 506 b, 508 a, and 508 b may have values that range between about two volts and about seven volts, or between about one volt and about four volts, or be equal to about one volt, about two volts, about three volts, about four volts, about five volts, about six volts, about seven volts, or any other suitable value. The specific amplitude values described with respect to the phasic conducted communication pulses may represent either peak amplitudes or Root Mean Square (RMS) amplitudes.

In some cases, the amplitudes 506 a, 506 b may not be equal to amplitudes 508 a, 508 b, respectively, but for differences in polarity. For instance, in at least some embodiments, amplitudes 506 a, 506 b may have values that are between about seventy-five percent and about ninety-nine percent of the values of amplitudes 508 a, 508 b, respectively. In still further embodiments, amplitudes 508 a, 508 b may have the smaller values. In still further additional or alternative embodiments, amplitudes 506 a, 506 b, 508 a, and/or 508 b may vary between successively delivered phasic conducted communication pulses. For instance, the values of amplitudes 506 a, 506 b, 508 a, and 508 b may vary by less than about ten percent between successively delivered phasic conducted communication pulses.

Alternatively, or in addition to that described above, it is contemplated that the amplitudes 505 a, 505 b of the abbreviated phases 505 a, 505 b may differ from the amplitudes 508 a, 508 b of unabbreviated phases 507 a, 507 b in order to help control charge accumulation on excitable tissue and reduce the likelihood that the unabbreviated phases 507 a, 507 b will stimulate the tissue. In one specific example, with reference to FIG. 5A, pulse width 502 a may be equal or about equal to pulse width 504 a, and the absolute value of the amplitude 506 a may be less than (e.g. abbreviated) the absolute value of the amplitude 508 a. In some cases, both the pulse width and amplitude of the abbreviated phases 505 a, 505 b and unabbreviated phases 507 a, 507 b may be set to help control charge accumulation on excitable tissue and thus reduce the likelihood that the unabbreviated phases 507 a, 507 b will stimulate the tissue.

Although FIGS. 5A-B depict bi-phasic conducted communication pulses 501, 503 with first phases 505 a, 505 b and second phases 507 a, 507 b having generally rectangular morphologies, it should be understood that the techniques of the present disclosure are not limited to these particular morphologies of first phases 505 a, 505 b and second phases 507 a, 507 b. FIGS. 6A-6D depict other illustrative pulses with different phase morphologies. FIG. 6A depicts a bi-phasic conducted communication pulse 512 with saw-tooth phases. FIG. 6B depicts a bi-phasic conducted communication pulse 513 with exponential phases. FIG. 6C depicts a bi-phasic conducted communication pulse 514 with trapezoid phases. FIG. 6D depicts a bi-phasic conducted communication pulse 515 with stepped phases. It is contemplated that bi-phasic conducted communication pulses that are substantially similar to these may be used. In this regard, a first pulse phase is considered substantially similar to a second pulse phase if the area between the first pulse phase and the second pulse phase is less than 10% of the area under the second pulse phase, with the amplitude and duration of the first pulse phase normalized to the second pulse phase. It should be understood that these are only example pulse shapes. It is contemplated that any suitable pulse shape may be used. In general, an abbreviated leading pulse may indispose the tissue to excitation (e.g. capture) by the successive pulse(s). In some cases, a trailing abbreviated pulse (e.g. see FIGS. 9A-9B, 10A-10B, 11A-11B) may be used for charge balance, or further excitation inhibition. It is contemplated that such pulses may have any suitable form of voltage or current vs time, as long as a leading pulse contributes charge to the tissue in a manner that inhibits excitation (e.g. hyperpolarization).

Although FIGS. 6A-D depict phasic conducted communication pulses having differing phase morphologies than the phase morphologies of FIGS. 5A-B, the two separate phases of each phasic conducted communication pulse of FIGS. 6A-D may have similar values to those described with respect to first phases 505 a, 505 b and second phases 507 a, 507 b. Notably, in FIGS. 6A-D, a first phase is shown preceding a second phase, with the duration of the first phase being abbreviated with respect to the second phase. Also, although each phasic conducted communication pulse 512-515 of FIGS. 6A-D is only shown with a single polarity orientation, it should be understood that phasic conducted communication pulses 512-515 may be implemented with the opposite polarity orientation, if desired. Moreover, it is contemplated that, in short pulse durations (e.g. less than 60 microseconds or less), a longer pulse may be provided first, followed by a shorter pulse to neutralize the charge on the tissue before activation of the tissue occurs.

FIGS. 7 and 8 depict different example communication schemes that may be used by devices of a system, such as system 400, with the phasic conducted communication pulses described with respect to FIGS. 5A-6D and elsewhere in this disclosure. For ease of description, only rectangular phasic conducted communication pulses are shown, but it should be understood that the disclosed techniques are independent of phasic conducted communication pulses morphology.

FIG. 7 shows a graph of four example phasic conducted communication pulses 530 a-d. Phasic conducted communication pulses 530 a-d are separated by three distinct time periods, 532, 534, and 536, respectively. In the example shown, the last time period 538 does not separate one communication pulse 530 d from another communication voltage pulse. Rather, time period 538 is simply a threshold length of time extending from communication pulse 530 d, without a subsequent communication voltage 530 occurring before the end of the threshold length of time. This can signal an end-of-frame (EOF).

In some cases, devices of a system using the phasic conducted communication pulses and the techniques described herein may identify communication symbols based on the length of time between phasic conducted communication pulses 530 a-d. For example, if the time between two consecutive phasic conducted communication pulses falls within a first time range, then a first symbol may be identified by the receiver. If the time between two phasic conducted communication pulses falls within a second time range, then a second symbol may be identified by the receiver. If the time between two phasic conducted communication pulses falls within a third time range, then a third symbol may be identified by the receiver, and so on. In one example, a sync symbol is identified when the time between two phasic conducted communication pulses falls within a range of 800-1100 microseconds, a “1” symbol is identified when the time between two phasic conducted communication pulses falls within a range of 550-700 microseconds, and a “0” symbol is identified when the time between two phasic conducted communication pulses falls within a range of 350-450 microseconds. In some cases, the “0” and “1” symbols correspond to “0” and “1” bits, respectively, as the devices of the system may operate in a base two number system. These are just examples. It is contemplated that any number of different symbols may be included in the communication protocol, with different symbols assigned to different times or time ranges. In some case, if a phasic conducted communication pulse is not followed by another phasic conducted communication pulse within a threshold amount of time (e.g. time period 538), an end or frame (EOF) symbol may be identified. The threshold amount of time (e.g. time period 538) may be, for example, 1250 microseconds or more.

In some cases, the time between phasic conducted communication pulses may be tracked using an internal clock. It is contemplated that the sending device may include an internal clock that oscillates at a clock frequency. Likewise, the receiving device may include an internal clock that oscillates at the same (or different) clock frequency. When so provided, each symbol to be communicated may be assigned a different number of clock cycles between phasic conducted communication pulses. For example, a synchronization symbol may be assigned 24 clock cycles, which for a clock frequency of 25.6 kHz, would correspond to a delay between phasic conducted communication pulses of about 938 microseconds. A range may be provided to help compensate for noise, temperature changes, voltage variances, clock drift, etc. The range may be, for example, +/−10%, or in the example given above, may be from about 844 microseconds to about 1032 microseconds. A “1” symbol may be assigned to 16 clock cycles, which for a clock frequency of 25.6 kHz, would corresponds to a delay between phasic conducted communication pulses of about 625 microseconds. A range may be provided around this figure to help compensate for noise, temperature changes, voltage variances, clock drift, etc. The range may be, for example, +/−10%, or in the example given above, may be from about 563 microseconds to about 688 microseconds. Likewise, a “0” symbol may be assigned to 10 clock cycles, which for a clock frequency of 25.6 kHz, would correspond to a delay between phasic conducted communication pulses of about 391 microseconds. A range may be provided around this figure to help compensate for noise, temperature changes, voltage variances, clock drift, etc.

To transmit a desired symbol, the sending device may provide a first phasic conducted communication pulse, then count the number of clock cycles that corresponds to the desired symbol (e.g. 16 clock cycles for a “1” symbol), and then provide a phasic conducted communication pulse. When the receiving device receives the first phasic conducted communication pulse, the receiving device may start counting internal clock cycles. When the second phasic conducted communication pulse is received, the receiving device may stop counting clock cycles. The receiving device may then compare the number of counted internal clock cycles to the number of clock cycles assigned to each symbol. When a match is found, the desired symbol is identified by the receiving device.

In some cases, the accuracy of the internal clocks in the sending device and/or receiving device may degrade over time. Due to this degradation, the devices of the system may begin to determine lengths of time differently with respect to absolute lengths of time, and possibly with respect to each other if the clocks of the devices degrade differently with respect to each other. Accordingly, in examples where time periods 532, 534, 536, and 538 are ranges of times, the devices of the system may still correctly interpret symbols even after some level of clock degradation.

In some cases, the devices of the system may be configured to reconfigure their internal clocks on a periodic or other basis. For example, a first device may broadcast a beginning calibration signal, an ending calibration signal, and the length of time between the two signals as determined by the broadcasting device. Each other device may then calibrate their internal clocks so that the time period between the two calibration signals is equal to the length of time sent by the broadcasting device. Such a reconfiguration may help ensure that a clock of a device does not drift too far relative to that of other devices of the system such that the device becomes functionally inoperative.

Whatever the exact lengths of time periods 532, 534, 536, and 538, in some examples, time period 532 may be longer than either of time periods 534 and 536. In such examples, this arrangement may prevent accidental transmission of one or more symbols from one device to another device, or a device interpreting noise as communication of one or more symbols. For instance, the devices of the system may transmit phasic conducted communication pulses to communicate a synchronization symbol before transmitting one or more other symbols, and receiving devices may ignore any other symbols received before receiving a synchronization symbol. In some situations, a receiving device may receive a first, true phasic conducted communication pulse but then receive noise after a length of time shorter than time period 532. If the noise is similar in morphology to a phasic conducted communication pulse, the receiving device may interpret the noise as a phasic conducted communication pulse. However, since the noise occurred after a shorter length of time than time period 532, even if the noise occurred at a length of time indicating a “0” symbol or a “1” symbol, the receiving device would ignore those symbols as the receiving device had not yet received a synchronization symbol. In this manner, the devices of the system may suppress erroneously transmitted or falsely interpreted symbols.

In some instances, a blanking period may be applied by the receiving device immediately following receiving each phasic conducted communication pulse. During the blanking period, the receiving device may ignore any received communication signals. This may help further reduce noise that might arise immediately after a phasic conducted communication pulse from being interpreted as a valid phasic conducted communication pulse. The blanking period may be anywhere between one-quarter to three-quarters the length of time period 532, or any other suitable length of time. In one example, the blanking period may be, for example about 250 microseconds. In some cases, the sending device may apply a similar blanking period, during and/or following the transmission of a phasic conducted communication pulse. Such a blanking period may help prevent the circuitry of the sending device, which senses for phasic conducted communication pulses from other devices, from sensing the phasic conducted communication pulses generated by the sending device.

In FIG. 7, the receiving device(s) of the system may identify the elapse time 532 between communication pulses 530 a and 530 b, and interpret that elapse time 532 as, for example, a synchronization symbol. Likewise, the receiving device(s) of the system may identify the elapse time 534 between communication pulses 530 b and 530 c, and interpret that elapse time 534 as, for example, a “1” symbol. Moreover, the receiving device(s) of the system may identify the elapse time 536 between communication pulses 530 c and 530 d, and interpret that elapse time 536 as, for example, a “0” symbol. In some cases, the receiving device(s) of the system may detect that communication pulse 530 d is not followed by another phasic conducted communication pulse within the threshold amount of time 538, and may interpret that as an End of Frame (EOF) symbol. This particular example is only illustrative, and it is contemplated that different symbols, different time delays and different sequences may be used, depending on the application.

In some examples, the devices of the system are continuously (although possibly punctuated by blanking periods) listening for phasic conducted communication pulses. That is, the devices of the system may not send out wake-up signals or establish specific communication connections before sending out phasic conducted communication pulses to other devices. Instead, the devices of the system may rely on synchronization pulses as a signal to the other devices of the system that the sending device is sending a message. In some cases, an EOF symbol may be a signal that the sending device has communicated the entire message.

In the example of FIG. 7, time periods 532, 534, 536, and 538 are depicted as being measured from a leading edge of each communication pulse 530. However, in other examples, time periods 532, 534, 536, and 538 may be measured off of other features of phasic conducted communication pulses 530. For instance, the devices of the system may measure time periods 532, 534, 536, and 538 from the trailing edge of phasic conducted communication pulses 530. In still other examples, the devices of the system may measure time periods 532, 534, 536, and 538 from the inflection point of phasic conducted communication pulses 530. Additionally, the devices of the system may not begin measuring a time period from a feature of phasic conducted communication pulses 530, for example the leading edge, until the amplitude of the phasic conducted communication pulse reaches a threshold level. In some cases, the devices of the system may measure time periods 532, 534, 536, and 538 from a zero-crossing point of phasic conducted communication pulses 530. These are just some examples.

In some of these embodiments, the devices of the system may ensure that the same total amount of positive magnitude energy (e.g. voltage or current) is delivered into the body of the patient during communication as negative magnitude energy. This may help ensure that the communication scheme is charge balanced. Although, in some embodiments, the communication scheme may not be charge balanced. A communication scheme may be considered substantially charge balanced where the total area under the curves of the positive magnitude phases of the phasic conducted communication pulses of a sent or received communication sequence are within ten percent, either above or below, the total area of the negative magnitude phases of the phasic conducted communication pulses of the sent or received communication sequence.

In order to effect a charge balanced, or substantially charge balanced, communication sequence, a sending device may invert the polarity of every other delivered phasic conducted communication pulse. For instance, in the example described above, phasic conducted communication pulse 530 a may look like phasic conducted communication pulse 501, and communication pulse 530 b may look like phasic conducted communication pulse 503, e.g. having opposite polarity compared to phasic conducted communication pulse 501. Accordingly, where phasic conducted communication pulses 530 a, 530 b have the same dimensions with respect to each of their respective phases, but flip the polarity of each of the phases, any string of an even number of phasic conducted communication pulses will be charge balanced, and any string of an odd number of phasic conducted communication pulses, while not perfectly charge balanced, will be substantially charge balanced. Alternatively, a last phasic conducted communication pulses may be appended to any string of an odd number of phasic conducted communication pulses to create an even numbered string.

FIG. 8 depicts another illustrative communication scheme that may be implemented with the phasic conducted communication pulses disclosed herein. Instead of varying the length of time between successive phasic conducted communication pulses, the scheme of FIG. 8 may use differences in the polarity of the phasic conducted communication pulses to encode information.

The example of FIG. 8 depicts a sequence of pulses 540. Sequence of pulses 540 includes phasic conducted communication pulses 541-544. Phasic conducted communication pulses 541 and 542 have a first polarity, with their first phases having a positive polarity and their second phases having a negative polarity, while phasic conducted communication pulses 543 and 544 have a second polarity with their first phases having a negative polarity and their second phases having a positive polarity. In the example of FIG. 8, one of the first or second polarities may be associated with a ‘0’ symbol, and the other of the first or second polarities may be associated with a ‘1’ symbol. In this manner, where the devices using the communication scheme of FIG. 8 operate according to binary number system, the devices may communicate information using sequences of phasic conducted communication pulses, which each phasic conducted communication pulse denoting either ‘0’ or ‘1’. For instance, in the example of FIG. 8 where the first polarity is associated with ‘0’ and the second polarity is associated with ‘1’, sequence of pulses 540 may read ‘0011’ according to this communication scheme.

As with the example of FIG. 7, it may be beneficial for a sent communication to be charge balanced or substantially charge balanced. However, in the example of FIG. 8, since the polarity of the phasic conducted communication pulses represents information, a sending device may not be able to use the charge balancing scheme described with respect to FIG. 7. Instead, a sending device may determine how many more phasic conducted communication pulses having one of the polarities the device sent than the other polarity. For instance, if the sending device sent a sequence of phasic conducted communication pulses including four phasic conducted communication pulses having the first polarity and two phasic conducted communication pulses having the second polarity, the device may determine that the device sent two more phasic conducted communication pulses having the first polarity than the second polarity. The sending device may then deliver a sequence of pulses including two phasic conducted communication pulses having the second polarity. The receiving device may know to ignore every other sequence of pulses delivered from a sending device as a charge balancing sequence. In some embodiments, the sending device may not send any charge balancing sequence of pulses if the difference between the number of pulses delivered having the first polarity and the second polarity (or having the second polarity and the first polarity) is below a threshold number of pulses. In these embodiments, the sending device may determine that the communicated sequence of pulses is substantially charge balanced such that no charge balancing sequence of pulses is necessary.

FIGS. 9A-B depict still further illustrative phasic conducted communication pulses, phasic conducted communication pulses 551, 553, that may be used in accordance with the present disclosure. Generally, phasic conducted communication pulses 551, 553 may be similar to phasic conducted communication pulses 501, 503 except that phasic conducted communication pulses 551, 553 include three phases instead of two.

As can be seen in FIGS. 9A-B, phasic conducted communication pulses 551, 553 include first phases 557 a, 557 b, second phases 558 a, 558 b, and third phases 559 a, 559 b. First phases 557 a, 557 b have abbreviated pulse widths 552 a, 552 b, while second phases 558 a, 558 b and third phases 559 a, 559 b having non-abbreviated pulse widths 554 a, 554 b and 556 a, 556 b. As in the embodiments of FIGS. 5A-B, abbreviated pulse widths 552 a, 552 b may have values that represent a portion of the values of non-abbreviated pulse widths 554 a, 554 b and 556 a, 556 b. In general, the values and proportions described with respect to abbreviated pulse widths 502 a, 502 b and pulse widths 504 a, 504 b of phasic conducted communication pulses 501, 503 may apply equally to abbreviated pulse widths 552 a, 552 b and non-abbreviated pulse widths 554 a, 554 b and 556 a, 556 b. However, in at least some embodiments, pulse widths 554 a and 556 a, and/or pulse widths 554 b and 556 b may not be equal. In some cases, this difference may between about one percent and about eighty percent, between about one percent and about fifty percent, about one percent and about thirty percent, about one percent and about ten percent. In some cases, pulse width 556 a may be less than pulse width 554 a by an amount that is about equal to abbreviated pulse width 552 a, and pulse width 556 b may be less than pulse width 554 b by an amount that is about equal to abbreviated pulse width 552 b.

Additionally, phases 557 a and 559 a of phasic conducted communication pulse 551 may have the same amplitude, amplitude 560 a, while phase 558 a has amplitude 555 a. In some embodiments, amplitudes 560 a and 555 a may be equal but opposite in magnitude (e.g. opposite polarity about neutral or ground). However, in other embodiments, amplitudes 560 a and 555 a may differ, sometimes by less than ten percent. In some cases, amplitudes 560 b and 555 b may be equal but opposite in magnitude (e.g. opposite polarity about neutral or ground). However, in other embodiments, amplitudes 560 b and 555 b may differ, sometimes by less than ten percent. In some cases, phases 557 a and 559 a may have the same or different amplitudes, but both still having positive magnitude amplitudes (e.g. same polarity). In some cases, the amplitudes of phases 557 a and 559 a may differ by less than ten percent

In each of the embodiments of FIGS. 5A-6B and FIGS. 9A-B, each of the disclosed phasic conducted communication pulses were not necessarily charge balanced. That is, each of the phasic conducted communication pulses may not include an area under those portions of the phasic conducted communication pulses that have a positive polarity do not necessarily equal those portions of the phasic conducted communication pulse that have a negative polarity. In some embodiments, it may be beneficial to employ inherently charge balanced phasic conducted communication pulses so that there is no need for charge balancing by counting differences between the delivered numbers of different polarity phasic conducted communication pulses or by flipping the polarity of each successively delivered phasic conducted communication pulse.

FIGS. 10A-B depict a quad-phasic phasic conducted communication pulse that is shown to be charge balanced. FIGS. 10A-B depict phasic conducted communication pulses 561, 563, respectively. Each of phasic conducted communication pulses 561, 563 has first phases 571 a, 571 b, second phases 573 a, 573 b, third phases 575 a, 575 b, and fourth phases 577 a, 577 b. Each of first phases 571 a, 571 b, second phases 573 a, 573 b, third phases 575 a, 575 b, and fourth phases 577 a, 577 b have a corresponding amplitude and pulse width. In the example shown, first phases 571 a, 571 b and fourth phases 577 a, 577 b have abbreviated pulse widths 562 a, 562 b and 568 a, 568 b, while second phases 573 a, 573 b and third phases 575 a, 575 b have non-abbreviated pulse widths 564 a, 564 b, and 566 a, 566 b. Generally, pulse widths 564 a, 564 b, and 566 a, 566 b may have values similar to those described with respect to other phasic conducted communication pulses described herein. Additionally, abbreviated pulse widths 562 a, 562 b and 568 a, 568 b may also have values, or proportions to pulse widths 564 a, 564 b, and 566 a, 566 b, similar to those values described herein with respect to other phasic conducted communication pulses. Additionally, amplitudes 565 a, 565 b, and 567 a, 567 b may have similar values to those amplitudes described with respect to previously described phasic conducted communication pulses.

Where abbreviated pulse widths 562 a, 562 b and 568 a, 568 b are equal to each other and pulse widths 564 a, 564 b, and 566 a, 566 b are equal to each other, phasic conducted communication pulses 561, 563 will be charge balanced as the areas under first phases 571 and fourth phases 577 will equal the areas under second phases 573 and third phases 575. However, in other embodiments, there may be variations between different phases of phasic conducted communication pulses 561, 563. In these embodiments, where there is a difference of less than ten percent between the areas under first phases 571 and fourth phases 577 and the areas under second phases 573 and fourth phases 577, phasic conducted communication pulses 561, 563 may still be considered substantially charge balanced. Over time, these small differences may not adversely impact the patient in which the devices using phasic conducted communication pulses 561, 563 are implanted.

Additional illustrative charged balanced phasic conducted communication pulses are depicted in FIGS. 11A-B. Phasic conducted communication pulses 581, 583 are hexa-phasic conducted communication pulses. Phasic conducted communication pulse 581 includes first phase 591 a, second phase 592 a, third phase 593 a, fourth phase 594 a, fifth phase 595 a and sixth phase 596 a. Phasic conducted communication pulse 583 583 includes first phase 591 b, second phase 592 b, third phase 593 b, fourth phase 594 b, fifth phase 595 b, and sixth phase 596 b. Each of these phases 591 a-596 a and 591 b-596 b include pulse widths 582 a, 582 b, 584 a, 584 b, 586 a, 586 b, 588 a, 588 b, 590 a, 590 b, and 597 a 597 b as shown. Further, each of phases 591 a-596 a and 591 b-596 b have amplitudes 585 a, 585 b or 587 a, 587 b also as shown.

In at least some embodiments, pulse widths 582 a, 582 b, 584 a, 584 b, 590 a, 590 b, and 597 a, 597 b may be abbreviated pulse widths, to one degree or another. For instance, abbreviated pulse widths 584 a, 584 b and 590 a, 590 b may have similar values and/or proportions to those described with respect to abbreviated pulse widths 502 a, 502 b. Abbreviated pulse widths 582 a, 582 b and 597 a, 597 b may have different values or proportions. For instance, abbreviated pulse widths 584 a 584 b and 590 a, 590 b may have values that range between about five percent and about eighty percent of the value of pulse widths 586 a, 586 b and/or 588 a, 588 b. In more specific embodiments, abbreviated pulse widths 582 a, 582 b and 597 a, 597 b may have values that range between about ten percent and about fifty percent of the value of pulse widths 586 a, 586 b and/or 597 a, 597 b or be about ten percent, about twenty percent, about twenty-five percent, about thirty percent, about forty percent, about fifty percent, or any other suitable percentage of the value of pulse widths 586 a, 586 b and/or 597 a, 597 b. Abbreviated pulse widths 582 a, 582 b and 597, on the other hand, may have values that range between about one percent and about twenty-five percent of the values of pulse widths 586 a, 586 b and/or 597 a, 597 b.

In a similar manner to phasic conducted communication pulses 561, 563, phasic conducted communication pulses 581, 583 may be charge balanced when the phases 591 a-593 a and 591 b-593 b having a first polarity are symmetrical with the corresponding phases 594 a-596 a and 594 b-596 b having a second opposite polarity. However, even in embodiments where the phases having the first polarity are not perfectly symmetrical with the phases having the second polarity, phasic conducted communication pulses 581, 583 may still be considered substantially charge balanced if the total area of the phases having the first polarity is within about ten percent of the total area of the phases having the second polarity.

The specific values for the pulse widths of the different disclosed phasic conducted communication pulses may be chosen based on a study carried out on a canine. FIG. 12 shows a graph 600 of data collected from a canine study showing heart capture threshold versus pulse width duration for various different communication pulse morphologies including mono-phasic, bi-phasic, and quad-phasic). It is desirable to not capture the heart of the canine with the communication pulses. As such, a higher capture threshold is desirable.

Graph 600 depicts lines 601, 603, 605, 607, 609, and 611 on a log-log plot of pulse widths (x-axis) versus the amplitude at which the pulse caused stimulation (i.e. capture) of the heart tissue. Line 601 represents results for a mono-phasic pulse having a first polarity (cathodic polarity) while line 603 represents results for a mono-phasic pulse having a second polarity (anodic polarity), which is opposite the first polarity. Lines 605 and 607 depict results for bi-phasic pulses having opposite polarities, and lines 609 and 611 depict results for quad-phasic pulses having opposite polarities.

The pulse width duration values of the x-axis of graph 600 represent the values for the non-abbreviated pulse width. For instance, with respect to the quad-phasic pulses, the pulse width duration values correspond to the values of pulse widths 564, 566 of quad-phasic pulses 561, 563. For the mono-phasic pulses, the pulse width duration equals the total pulse width of the entire pulse. For the bi-phasic pulses, the pulse width duration values correspond to one half of the total pulse width, as the biphasic pulses used in the study had two equal duration phases, unlike the bi-phasic pulses of the present disclosure that have an initial pulse width an abbreviated pulse width. For the quad-phasic pulse, the first and fourth phases had abbreviated pulse widths relative to the second and third phases. The second and third phases had substantially equal pulse widths, and the first and fourth phases had pulse widths of about one-half the pulse widths of the second and third phases.

As can be seen in graph 600, at relatively long pulse widths in region 602, the different pulses all cause stimulation of heart tissue at relatively similar amplitudes, e.g. between about 500 mV and about 1 V, with the mono-phasic cathodic pulses having the highest amplitude that does not cause simulation. In this region, the pulse widths are between about 250 microseconds to about 500 microseconds.

Beginning in region 604, the amplitudes at which the different pulses cause stimulation of the heart begin to separate. For instance, particularly between pulse lengths of about 75 microseconds and about 50 microseconds there is clear separation in the amplitudes at which the different pulses cause stimulation. As can be seen, both quad-phasic pulses have overtaken the other pulses in terms having the highest amplitudes, which are still not stimulating at pulse widths of about 60 microseconds.

By the time the pulse widths go down to between 25 microseconds or 20 microseconds and 5 microseconds, the differences between the amplitudes required before the quad-phasic pulses cause stimulation and the other pulses cause stimulation is significant. For example, at 6 microseconds, the quad-phasic pulses require around 40 V in order to cause stimulation of the heart, while the bi-phasic pulses only require around 20 V or 22 V. The mono-phasic pulses in this pulse width range require only between 9-11 V to be stimulating.

In some cases, it is contemplated that the electrical stimulation pulses, which are meant to capture the heart, may be delivered using a first polarity, and the communication pulses, which are not meant to capture the heart, may be delivered using a second opposite polarity. For example, in the example LCP 100 shown in FIG. 1, the pulse generator module 104 may deliver electrical stimulation pulses using electrodes 114. In the example shown, electrodes 114 include a smaller electrode on the left end of the LCP 100 and an annular surface electrode toward the right side of the LCP 100. The smaller electrode on the left end of the LCP 100 may have a significantly smaller surface area than the larger annular surface electrode toward the right side of the LCP 100. Thus, when an electrical pulse is delivered between these two electrodes, the current density at the smaller electrode on the left end of the LCP 100 is higher than the current density at the larger annular surface electrode. As such, it is often desirable to place the smaller electrode adjacent or in contact with the heart tissue to reduce the energy required to capture the heart. When so provided, the polarity of the electrical stimulation pulses may be delivered such that the smaller electrode functions as the cathode and the larger annular surface electrode toward the right side of the LCP 100 functions as the anode.

While it is desirable to reduce the energy required to capture the heart (i.e. reduce the capture threshold) when delivering electrical stimulation therapy, it is often desirable to increase the energy required to capture the heart (i.e. increase the capture threshold) when delivering communication pulses. As such, and in some cases, the polarity of the communication pulses may be delivered such that the smaller electrode on the left end of the LCP 100 functions as the anode and the larger annular surface electrode toward the right side of the LCP 100 functions as the cathode. Alternatively, or in addition, the pulse width duration of the communication pulses may be less than the pulse width duration of the electrical stimulation pulses. As shown in FIG. 12, there may be a significant difference between the capture thresholds when applying pulses in an anodic polarity versus a cathodic polarity, especially for monophasic pulses with pulse width durations of less than about 60 microseconds. In some cases, the electrical stimulation pulses may be delivered using a cathodic polarity with a pulse width duration of greater than 60 microseconds, and the communication pulses may be delivered using an anodic polarity with a pulse width duration of less than 60 microseconds. This is just one example.

It is believed that the first phase of the disclosed bi-, tri-, quad-, and other multi-phasic pulses having first phases with abbreviated pulse widths pre-load the tissue (e.g. heart) in an opposite manner to how the second longer phase loads the heart. That is, depending on the polarity of the first phase, the first phase may draw charge to or push charge away from heart cells. This mechanism may be in direct opposition to how the second phase of the pulse causes the charges near the heart cells to act. Accordingly, this pre-loading may allow for longer pulse width durations (e.g. longer pulse widths in subsequent phases of a pulse) or higher amplitudes to be used for communication pulses without fear of accidentally causing unwanted stimulation of the heart or other tissue. Or, the pre-loading may enhance the safety margin with which a system operates when using conducted communication pulses as it increases the amplitudes at which the communication pulses would cause stimulation. Allowing the use of relatively greater energy communication pulses, without causing unwanted tissue stimulation, may enhance the ability of a receiver to receive the communication pulses, and increasing the safety margin of communication pulses with respect to their stimulating amplitude thresholds.

As detailed above, and in some cases, one or both the pulse width and amplitude of the various abbreviated phases and unabbreviated phases in FIGS. 5A-5B, 6A-6D, 9A-9B, 10A-10B and 11A-11B may be set to help control charge accumulation on excitable tissue and thus reduce the likelihood that the unabbreviated phases will stimulate the tissue.

Those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. For instance, as described herein, various embodiments include one or more modules described as performing various functions. However, other embodiments may include additional modules that split the described functions up over more modules than that described herein. Additionally, other embodiments may consolidate the described functions into fewer modules.

Although various features may have been described with respect to less than all embodiments, this disclosure contemplates that those features may be included on any embodiment. Further, although the embodiments described herein may have omitted some combinations of the various described features, this disclosure contemplates embodiments that include any combination of each described feature. Accordingly, departure in form and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended claims. 

What is claimed is:
 1. An implantable medical device for implantation into a patient, comprising: a housing; a pulse generation circuit disposed at least partially within the housing; a plurality of electrodes electrically coupled to the pulse generation circuit, the plurality of electrodes being exposed external to the housing; and a controller operatively coupled to the pulse generation circuit, the controller configured to: command the pulse generation circuit to deliver a sub-threshold phasic conducted communication pulse via at least two of the plurality of electrodes; wherein the sub-threshold phasic conducted communication pulse comprises a first phase having a first polarity followed by a second phase having an opposite second polarity; the second phase having a duration of less than 60 microseconds; and the first phase having a duration of between five percent and eighty percent of the duration of the second phase.
 2. The implantable medical device of claim 1, wherein the first phase has a first phase amplitude, with the absolute value of the first phase amplitude between 1 and 15 volts.
 3. The implantable medical device of claim 1, wherein the second phase has a second phase amplitude, with the absolute value of the second phase amplitude between 1 and 15 volts.
 4. The implantable medical device of claim 1, wherein the first phase has a first phase amplitude with an absolute value of between 2 and 7 volts, and the second phase has a second phase amplitude with an absolute value of between 2 and 7 volts.
 5. The implantable medical device of claim 4, wherein the first phase has a first phase amplitude with an absolute value of between 1 and 4 volts, and the second phase has a second phase amplitude with an absolute value of between 1 and 4 volts.
 6. The implantable medical device of claim 5, wherein the second phase has a duration of less than 30 microseconds.
 7. The implantable medical device of claim 5, wherein the second phase has a duration of less than 20 microseconds.
 8. The implantable medical device of claim 1, wherein the first phase has a duration of between forty percent and sixty percent of the duration of the second phase.
 9. The implantable medical device of claim 1, wherein the first phase and the second phase are each a substantially rectangular pulse.
 10. The implantable medical device of claim 1, wherein the first phase and the second phase are each substantially a rectangular pulse, a saw tooth pulse, an exponential pulse, a trapezoid pulse, or a stepped pulse.
 11. A medical device, comprising: a housing; a pulse generation circuit disposed at least partially within the housing; a plurality of electrodes electrically coupled to the pulse generation circuit, the plurality of electrodes being exposed externally to the housing; and a controller operatively coupled to the pulse generation circuit, the controller configured to: command the pulse generation circuit to deliver a sub-threshold phasic conducted communication pulse via at least two of the plurality of electrodes; wherein the sub-threshold phasic conducted communication pulse comprises at least three phases of alternating polarity; the duration of the second phase is less than 60 microseconds; and the duration of the first phase of the sub-threshold phasic conducted communication pulse is between five percent and eighty percent of the duration of the second phase of the sub-threshold phasic conducted communication pulse.
 12. The medical device of claim 11, wherein the sub-threshold phasic conducted communication pulse comprises a first phase, a second phase and a third phase, with each phase having a duration and an amplitude, and wherein the first phase and the third phase have a first polarity and the second phase has a second opposite polarity.
 13. The medical device of claim 12, wherein the duration of the second phase is less than 50 microseconds, and the duration of the first phase is between forty percent and sixty percent of the duration of the second phase.
 14. The medical device of claim 11, wherein the sub-threshold phasic conducted communication pulse is substantially charge balanced.
 15. The medical device of claim 11, wherein the sub-threshold phasic conducted communication pulse has four or more phases, each of the four or more phases having a duration.
 16. A medical device comprising: a housing; a plurality of electrodes coupled to the housing; and a communication circuit electrically connected to the plurality of electrodes, the communication circuit configured to: deliver a sub-threshold phasic conducted communication pulse via two or more of the plurality of electrodes for communicating information external to the medical device; wherein the sub-threshold phasic conducted communication pulse comprises a first phase, followed by a second phase, followed by a third phase; the first phase and the third phase having a first polarity, and the second phase having an opposite second polarity; the second phase has a duration of less than 60 microseconds, and the first phase has a duration of between five percent and eighty percent of the duration of the second phase. 